Turns out it’s possible to make a fast-food lunch a bit healthier even without skipping the fries.

New York City now has hard evidence that its ban on trans fat in restaurant food made a meaningful dent in people’s consumption of the artery clogger and wasn’t just replaced with another bad fat.

The findings being published Tuesday have implications beyond heart health, suggesting another strategy to curb the nation’s obesity epidemic fueled by a high-calorie, super-sized environment.

Consider: Americans get more than a third of their daily calories from foods prepared outside the home. By year’s end, the Food and Drug Administration hopes to finalize long-awaited rules that would make many restaurant chains post the calorie counts of their products right on the menu.

Maybe the guilt would make you forego the french fries for a salad. Maybe not.

Now contrast New York’s trans-fat ban — later copied by more than a dozen other state and local governments — which didn’t put all the onus on the consumer to do the right thing.

“By making the default option the healthier choice,” everyone benefits regardless of their nutrition awareness or willpower, Alice Lichtenstein, a nutrition specialist at Tufts University, wrote in a commentary on the research. “The regulation may serve as a model for future successful public health initiatives.”

There are good fats and bad fats.

Trans fat is widely considered the worst kind for your heart, gram-for-gram more harmful than its better known cousin, saturated fat. Small amounts occur naturally in some meat and dairy products. But much of the trans fat we eat is artificially produced, by hardening liquid oils so they can be used for baking or a longer shelf life.

In 2006, the federal government began requiring that packaged foods list the amount of trans fat contained per serving, a boon for grocery shoppers who could finally tell which processed foods were more or less heart-healthy.

But restaurant fare remained a mystery. So New York City issued a first-of-its-kind rule restricting artificial trans fat in restaurants, forcing them to alter recipes so that foods contained no more than 0.5 grams per serving. The change affected customers beyond New York as big chains like McDonald’s wound up cutting the fat system-wide.

The latest study by the New York City Department of Health and Mental Hygiene shows the effect. Researchers surveyed customers and collected receipts for nearly 15,000 lunchtime purchases at fast-food chains around the city in 2007 and 2009, before and after the ban was in place.

The amount of trans fat in each lunch sold dropped an average of 2.4 grams after the ban, researchers report in Tuesday’s edition of Annals of Internal Medicine. The biggest drop, 3.8 grams, occurred in hamburger chains, followed by Mexican food and fried chicken chains.

No one’s saying that turned junk food into health food. But for people who eat fast food regularly, it’s a significant reduction in heart risk, said Margo Wootan, director of nutrition policy at the advocacy group Center for Science in the Public Interest.

The American Heart Association has long recommended that people limit trans fat to less than 2 grams a day. The newest government dietary guidelines urge people to eat as little trans fat as possible.

Moreover, the study also suggests that restaurants didn’t just swap out one bad ingredient for another as some nutritionists had feared. It found only a small increase in saturated fat, mostly in sandwich chains. That’s at least partly due to those customers buying meals with a lot more calories in 2009 than before, said study co-author Christine Curtis. That time period saw Subway’s introduction of $5 foot-long subs.

Overall, Americans’ trans fat consumption has dropped by more than half over the last decade, thanks to the combination of nationwide food-labeling and community restaurant restrictions, according to an update published in the Journal of the American Medical Association this month.

Still, 10 percent of children and adults consume more than 2.6 grams of industrially produced trans fats a day — not counting the natural type, said that review by researchers at the Centers for Disease Control and Prevention. Those people tend to consume certain brands of frozen pizza, frozen desserts, microwave popcorn and chips that still pack in the trans fat.

The trans-fat evolution shows that “no one policy is going to be the cure-all” for nutrition ills, said CSPI’s Wootan.

She points to the upcoming menu calorie counts. New York City already requires calories to be posted on menus, and a study found only 15 percent of diners ordered healthier foods. But those who did cut 100 calories per meal, which adds up fast, Wootan noted.

And peer pressure should make restaurants revamp recipes to cut calories, just like posting trans fat on grocery food labels pushed manufacturers to improve those offerings, she added.

Stay tuned on the calorie front: The FDA’s menu-labeling rules were expected months ago. There’s been a lobbying fight over whether they should include how many calories are in alcoholic drinks or in foods sold in places like movie theaters, where a tub of popcorn can total half your day’s allotment.

But Wootan would like to see additional options that make the lower-calorie choice the default. Why shouldn’t the fast-food meal-deal come with fruit, so you have to order the fries separately if you really want them?

“Right now the automatic choice, the easy choice, is the unhealthy option. If it were turned around, many more people would eat healthfully,” she said.